Why Electrochemical–Thermal–Mechanical Understanding is Needed to Explain Knees in Lithium-Ion Batteries Degradation
6 affiliations
- 1Department of Mechanical Engineering, Imperial College London, Exhibition Road, London, United Kingdom, SW72AZ
- 2Faraday Institution, Quad One, Becquerel Avenue, Harwell Campus, Didcot, United Kingdom, OX11 0RA
- 3Brackley, United Kingdom, NN13 7UG
- 4Dyson School of Design Engineering
- 5Imperial College London
- 6Harwell Science and Innovation Campus, Finden Ltd, Building R70, United Kingdom, OX11 0QX
Abstract
Lithium-ion batteries are essential to modern life, spanning portable electronics, electric vehicles and grid storage. Yet, their degradation mechanisms remain incompletely understood, particularly the sudden capacity drops known as knee points. In this study, commercial Samsung 50S cells are degraded under various cooling setups and charge/discharge rates, revealing consistent knees in slow-discharge cells even above 80% of initial capacity, while fast-discharge cells degraded beyond 60% without knees. Using a multiphysics characterisation approach, we decipher the origins of these knees: attainment of lower voltages enhances silicon activity, triggering a chain of mechanisms that culminate in sudden failure. Specifically, recurring SEI reformation drives a dual pathway: gas release displaces electrolyte, inducing localised current concentration, overcharge and a first pattern of lithium plating, while simultaneous electrode thickening deforms the jelly roll. This mechanical effect, combined with geometrical heterogeneities from the welded tab design, produces a second pattern of lithium plating in later ageing states, identified as the primary cause of the knees. These findings elucidate the complex coupling of multiscale degradation mechanisms and demonstrate that robust state-of-health monitoring must be holistic, incorporating indicators beyond traditional temperature, capacity and resistance.
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BibTeX
@misc{souza2026electrochemicalthermalmechanical,
title = {{Why Electrochemical–Thermal–Mechanical Understanding is Needed to Explain Knees in Lithium-Ion Batteries Degradation}},
author = {Matheus Leal de Souza and M. Waseem Marzook and Mohammed Asheruddin N and Derek Siu and Antonis Vamvakeros and Gregory Offer and Monica Marinescu},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15009177/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009177/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Why Electrochemical–Thermal–Mechanical Understanding is Needed to Explain Knees in Lithium-Ion Batteries Degradation
AU - Matheus Leal de Souza
AU - M. Waseem Marzook
AU - Mohammed Asheruddin N
AU - Derek Siu
AU - Antonis Vamvakeros
AU - Gregory Offer
AU - Monica Marinescu
PY - 2026
DA - 2026/09/21
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009177/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009177/v1
AB - Lithium-ion batteries are essential to modern life, spanning portable electronics, electric vehicles and grid storage. Yet, their degradation mechanisms remain incompletely understood, particularly the sudden capacity drops known as knee points. In this study, commercial Samsung 50S cells are degraded under various cooling setups and charge/discharge rates, revealing consistent knees in slow-discharge cells even above 80% of initial capacity, while fast-discharge cells degraded beyond 60% without knees. Using a multiphysics characterisation approach, we decipher the origins of these knees: attainment of lower voltages enhances silicon activity, triggering a chain of mechanisms that culminate in sudden failure. Specifically, recurring SEI reformation drives a dual pathway: gas release displaces electrolyte, inducing localised current concentration, overcharge and a first pattern of lithium plating, while simultaneous electrode thickening deforms the jelly roll. This mechanical effect, combined with geometrical heterogeneities from the welded tab design, produces a second pattern of lithium plating in later ageing states, identified as the primary cause of the knees. These findings elucidate the complex coupling of multiscale degradation mechanisms and demonstrate that robust state-of-health monitoring must be holistic, incorporating indicators beyond traditional temperature, capacity and resistance.
ER -